1. Field of the Invention
The present invention relates generally to downhole tools used in performing wellbore operations. More specifically, the present invention relates to techniques for determining downhole parameters via a retrievable downhole while-drilling tool.
2. Background of the Related Art
The harvesting of hydrocarbons from subterranean formations involves the drilling of wellbores into the earth. To create the wellbore, a downhole drilling tool is suspended from a drilling rig and advanced into the earth via a drill string. During the drilling operation, it is desirable to obtain information about the downhole conditions. Such information is useful, for example, in locating desirable formations, preventing potential problems and improving the drilling operation.
Downhole drilling tools are typically provided with a bottom hole assembly (BHA) that consists of one or more drill collars with various instruments therein. One such instrument (or combination of instruments) typically positioned in the BHA is a measurement while drilling (MWD) or logging while drilling (LWD) tool (referred to collectively herein as while drilling or WD tools). WD tools typically include a combination of sensors, telemetry devices, power supplies and/or other instruments, for performing various downhole functions, such as taking downhole measurements, compiling information about the drilling operation and communicating with the surface. Examples of existing MWD tools and systems are described in U.S. Pat. No. 5,357,483 assigned to Halliburton, U.S. Pat. No. 5,517,464 assigned to the assignee of the present invention and U.S. Application No. 20030080743 assigned to Baker Hughes. Examples of LWD tools are described in U.S. Pat. No. 4,899,112, assigned to the assignee of the present invention. Some such WD tools are also retrievable and replaceable from the downhole drilling tool as described, for example, in U.S. Pat. No. 6,577,244, assigned to the assignee of the present invention. At least some such WD tools may be vulnerable to leakage, seal failure about orifices extending through the drill collar and/or otherwise lack reliability or performance capabilities in a variety of wellbore environments.
Current WD tool and associated instruments (WD systems) are typically housed within steel, cylindrical and hollow drill collars to protect them from moisture, temperature, chemical and/or pressure exposure. However, it is desirable to position certain instruments, such as sensors, in such a way that they are capable of taking more precise measurements without increasing the potential risk of damage and/or exposure to the remainder of the WD system. The risk of leakage and/or damage may increase in situations where ports extend through the drill collars and into the WD system. It is therefore desirable that the downhole drilling tool be further capable of one or more of the following, among others: retreivability from the drilling tool, resetability in the drilling tool, wireless communication between instruments, isolation of certain components from wellbore conditions, retrieval of certain components to the surface for replacement, maintenance and/or adjustment and/or resistance to leakage. Moreover, such a system preferably optimizes drilling performance, reduces drilling time and assists in increasing rate of penetration and accuracy of well placement in drilling environments.
It is further desirable that the drilling tool be capable of performing in even extremely harsh wellbore conditions. The downhole drilling of wellbores, such as oil wells, involves extreme operating conditions, such as high temperatures, high pressure and rigorous physical impact. Much of the drilling occurs at extreme depths into the Earth's surface or deep below the sea bottom. The environment encountered by downhole oil exploration tools can be very severe. Temperatures up to and in excess of 200 degree C. and pressures up to 1.38×108 Pa are not uncommon. Consequently, producers of oil exploration tools seek to design robust tools that can operationally sustain harsh conditions for extended lengths of time.
Perhaps the most challenging of all conditions is to design electronics that can reliably operate in high temperature environments. Standard electronic components are usually rated to operate only up to approximately 125 degree C. Thus, it becomes necessary to create or experimentally find electric components that can survive the high temperatures existing downhole.
Various downhole instruments have been developed to deal with certain high temperature or high pressure conditions. For example, there are MWD tools specified to 150 degrees C. that provide real-time inclination and gamma ray. There are also MWD tools specified to 175 degrees C. that can operate under certain conditions for certain applications. However, no known commercial MWD tools that are capable of operating above 175 degrees C. for extended periods of time offer desirable operational features, such as real-time gamma ray, retrievability and resetability, as well as vibration detection.
Attempts have been made to develop downhole tools with desirable capabilities for use in high temperature conditions. By way of example, one downhole tool has been rated at 180 degrees C. with survivability to 200 degrees C., but lacks continuous inclination and fishability. The reliability of such a tool has not yet been verified as operational in wells exceeding 170 degrees C. Another tool is rated to 200 degrees C., but it lacks gamma ray, continuous inclination, annular pressure and fishability, and is purported to suffer from poor reliability and low up-hole communication rate. In addition the electronics are typically discarded once they exceed 175 degrees C., this despite the use of 225 degrees C. silicon-on-insulator (SOI) components.
Electronic components are considered one of the major hurdles to high temperature MWD tools as there are only a few 200 degrees C. components commercially available. Those that are available typically fall into three major categories: (1) legacy ceramic components developed mostly for the military market that serendipitously work at high temperature, (2) multi-chip modules developed (or that can be developed) by end users and others using die known to work at high temperatures and (3) a few very basic and very expensive silicon-on-insulator (SOI) components developed specifically for the 200 degrees C. or greater market.
Attempts are being made to develop a process capable of producing very high temperature digital and mixed analog/digital devices. While such attempts offer exciting prospects for the long term, products remain unavailable for commercial processes. Individual components have yet to be developed, and pose significant costs.
A need also remains for a new retrievable and resetable WD tool. The capability for retrievability and repeatability provide a significant improvement over existing technologies since tools that fail in harsh environments can be removed and replaced with wireline, obviating the need for a long and expensive pipe-trip out of the hole and back in again.
It is desirable that the tool be capable of performing continuous inclination, downhole vibration detection, annular pressure and gamma ray detection, real time annular and/or internal pressure while drilling, real time continuous inclination, real time gamma ray detection, real time vibration monitoring, high speed operation, high power system controller/signal processing, high speed data acquisition, gamma ray measurement and acquisition, and/or pressure measurement and/or resealing capability for pressure acquisition, all for extended periods of time and under even high-temperature, high-pressure conditions. It is further desirable that such a tool and related components, such as sensors, electronics, packaging, materials and pressure housings, be operable in the areas of high temperature of at least about 175 degrees C., and preferably above at least about 200 degrees C. at pressures at least about 20 Kpsi (1406.5 kg/cm).
A need therefore exists for a WD system with one or more of these advanced capabilities.